A photodetector such as a photomultiplier tube to be used in a scanning electron microscope (SEM), a time of flight mass spectrometer (TOF-MS), or the like adopts a configuration in which a scintillator for converting an accelerated electron into light is provided at a preceding stage of the photodetector.
For example, the scanning electron microscope enables acquisition of images by accelerating secondary electrons from an observation object with acceleration voltage of about 12 kV, causing the electrons to be incident on a scintillator, and converting scintillation light generated in the scintillator into electric signals by a photodetector. In order to enhance throughput in such a device, it is necessary to increase electron scanning rate, and at the same time, reduce a fluorescence lifetime (decay characteristic) of scintillation light generated in the scintillator.
Further, in the time of flight mass spectrometer, mass spectrometry of ions is performed as follows, ions as a mass spectrometry object are converted with a micro channel plate (MCP) into electrons, the electrons are converted by a scintillator into light, and the generated scintillation light is further converted by a photodetector into electric signals, and time difference is measured. Similarly in such a device, it is necessary to reduce a fluorescence lifetime of scintillation light in the scintillator.